<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }
        
        .container {
            width: 500px;
            height: 400px;
            background-color: skyblue;
            margin: 0 auto;
            padding: 10px 50px;
            box-sizing: border-box;
        }
        
        .childern {
            width: 100%;
            height: 100%;
            background-color: pink;
        }
    </style>
</head>

<body>
    <div class="container">
        <div class="childern"></div>
    </div>
</body>

</html>